Sexual orientation is the durable pull of your emotional, romantic, and sexual attraction toward other people — or toward none.
Orientation is the direction your desire keeps pointing, over time, without you having to steer it. Psychologists tend to split it into three things that don't always line up: who you're attracted to, who you actually get with, and what you call yourself. A woman married to a man for thirty years can still be a lesbian. A guy who's only ever hooked up with guys might call himself straight. The label is yours to claim; the pull underneath it usually isn't up for negotiation.
That gap is why "orientation" beat "preference." A preference is a choice — oat or cow, techno or house. Sexologist John Money pushed "orientation" precisely because attraction doesn't work like a bar menu; you don't wake up and decide who does it for you. Decades of research back him up: hardly anyone recalls a moment of deciding, and nobody has found the single switch that sets it. "Sexual preference" still gets used, and it still lands as a small insult — it smuggles in the idea that you could pick differently if you just tried harder.
Orientation also isn't a fixed pair of boxes. It runs along a spectrum — from only-the-other-sex to only-the-same, with everyone in between, and plenty of people living outside the men/women frame altogether. And it's a different question from gender identity: who you are is one axis, who you want is another. On our floor both come up, usually around 4am, usually mid-sentence. You don't owe anyone a fixed answer — but knowing your own is a decent place to dance from.