Quota attainment is the percentage of your quota you actually hit in a given period. If your target is $100,000 and you close $80,000, you are at 80% attainment. It is the single most important number on a salesperson's record because it drives your OTE, your commission, your accelerator eligibility, and — most of all — your credibility when you forecast or ask for more territory.
In plain English
Attainment is the report card. Managers care less about how busy you were and more about what percentage of the target you produced. Consistently above 100% makes you a top performer; consistently under 80% puts your role at risk regardless of how hard you work.
Why it matters to you
Attainment is what recruiters and hiring managers actually ask about, usually as a trailing figure like "110% for the last three quarters." It is more persuasive than any activity number. During your ramp, attainment is measured differently, so ask how your target scales — and protect your record by only taking roles with realistic quota. If sales enablement is weak, attainment will suffer no matter how hard you push.
For pacing to the number, see Hit Your Sales Quota.