A write-up is a short written piece about something, published where other people will read it — a review of a restaurant, a report on a concert, a paragraph in the paper about a new phone or a school sports day. It is a countable noun with a hyphen, and it feels friendly and informal, the word you use rather than the grander "review" or "critique". The verbs that go with it tell you a lot: something "gets" or "receives" a write-up, a newspaper "gives" it one, and people constantly add a judging word in front — a good write-up, a glowing write-up, a terrible write-up. "Did you see the write-up in the paper?" almost always means a favourable one; if it were bad, the speaker would say so. There is a second, quieter use in offices, labs and schools: the write-up is the written version of work you have already done — "I've finished the experiment, now I just need to do the write-up." Both come from the same idea, that write up means to take rough notes or raw events and turn them into a proper piece of writing. Stress the first part: WRITE-up.