Two letters, five meanings. If you have ever paused at the abbreviation PO — on an invoice, a prescription, or a chat message — you are not alone. PO is one of those shortcuts that only makes sense once you know the setting it appears in. This guide walks through every common PO meaning, so you can spot the right one in seconds.
What Does PO Mean?
PO is an abbreviation with several unrelated meanings. The correct one depends entirely on where you see it. Here is a quick reference to the five you are most likely to run into:
| Abbreviation | Meaning | Where you will see it |
|---|---|---|
| PO | Purchase Order | Business, invoices, procurement |
| PO / p.o. | Per os (“by mouth”) | Prescriptions, medical charts |
| po | A word of respect | Filipino conversations |
| P.O. | Post Office | Mailing addresses, P.O. box |
| PO | Petty Officer | Military and naval contexts |
Below, each meaning is explained in detail with real examples, so you never have to guess again.
PO in Business: Purchase Order
This is the most common PO meaning by a wide margin. A purchase order is a document a buyer sends to a supplier before goods or services are delivered. It spells out exactly what is being bought: product descriptions, quantities, agreed prices, delivery dates, and payment terms.
A purchase order protects both sides. The buyer keeps a written record of what was ordered and at what price; the seller has proof of what was agreed before starting work. Once the supplier accepts it, the PO normally becomes a binding commitment — which is why companies track every PO by number and match it against the invoice before paying.
A simple example: a café ordering 200 paper cups sends its supplier a PO showing the cup type, quantity, unit price, delivery date, and payment terms. Nothing is left to memory or a verbal promise.
If you deal with suppliers or clients, it is worth understanding the full process — from raising a PO to avoiding the mistakes that cause payment delays. Read our detailed walkthrough: The Ultimate Guide to PO (Purchase Order): Process, Tips & Mistakes to Avoid.
PO in Medicine: Per Os
On prescriptions and in medical notes, PO stands for the Latin per os — “by mouth.” It tells the patient to take the medicine orally rather than by injection, cream, or any other route.
For example, “take one tablet PO twice daily” means swallow one tablet by mouth, morning and evening. You may also see it written as p.o. with periods — it means the same thing.
Most patients never notice this abbreviation, but pharmacists and doctors write it constantly. If any instruction on a prescription confuses you, ask the pharmacist — never guess at dosage directions.
PO in the Filipino Language
In the Philippines, po is not an abbreviation at all — it is a word in its own right, and an important one. Added to a sentence, it signals respect toward the person being spoken to.
Filipinos use it with elders, teachers, parents, and customers. Salamat po means “thank you” with respect; opo is a respectful way to say yes; magandang umaga po is “good morning” said politely. You will hear it everywhere from family homes to shops and call centers.
Skipping it is not rude among close friends, but using it is always noticed and appreciated. For a visitor to the Philippines, this one small word goes a long way.
Other Common Meanings of PO
Beyond the big three, PO shows up in a few more places worth knowing.
Post Office (P.O. Box)
In addresses, P.O. stands for Post Office — as in “P.O. box,” the lockable mailbox rented at a post office branch. It is the reason many businesses list a P.O. box instead of a street address.
Petty Officer
In naval forces, including the US and UK navies, PO is the standard abbreviation for Petty Officer, a non-commissioned officer rank. You will see it in military records, service documents, and news reports.
What PO Means Online and in Slang
The honest answer: online, PO has no single agreed meaning. People use it as initials, a nickname, or shorthand inside a specific group or game. Unlike the business and medical meanings, these uses are invented on the spot and only make sense to that community.
If you see PO in a chat and the context does not fit any meaning above, it is probably a personal or group-specific abbreviation. Internet shorthand shifts fast — our guide to another tricky abbreviation, what FS means in slang, shows how quickly these meanings change.
How to Tell Which PO You Are Looking At
Match the setting to the meaning:
- An invoice, order email, or accounting software → Purchase Order
- A prescription or medical chart → per os (by mouth)
- A Filipino conversation → the respect word po
- A mailing address → Post Office
- A military document → Petty Officer
Nine times out of ten, the setting gives it away before you finish the sentence.
Examples of PO in Sentences
- Business: “Please approve the PO so we can place the order today.”
- Medicine: “Take the capsule PO with a full glass of water.”
- Filipino: “Salamat po for helping us.”
- Address: “Send the form to P.O. Box 214.”
Frequently Asked Questions
What does PO stand for?
Most often, Purchase Order. In medicine it means per os (“by mouth”), in Filipino it is a word of respect, and in addresses it stands for Post Office.
Is PO always capitalized?
No. Business and medical writing usually capitalizes it (PO or P.O.), while the Filipino word is written lowercase (po).
What is the difference between a PO and an invoice?
A purchase order comes first — the buyer sends it to request goods. An invoice comes later — the seller sends it to request payment. Our purchase order guide explains the full sequence.
What does PO mean on a prescription?
It is shorthand for the Latin per os, meaning “by mouth” — take the medicine orally.
Does PO mean anything in texting?
There is no standard texting definition. In chats it is usually initials, a nickname, or group slang — the surrounding conversation is your best clue.
Final Word
PO is short, but it does a lot of work: a business commitment, a medical instruction, a word of respect, and a mailbox. Once you know the setting, the meaning is rarely a mystery.
