Keyword optimization
Also called resume keywords, keyword matching.
Using the employer's own vocabulary for skills and tools you genuinely have, so you appear in the searches a recruiter runs.
Recruiters find candidates inside an ATS by searching. If a posting says "Kubernetes" and your resume says "container orchestration", you're absent from that result set even though you're qualified. That is the entire mechanism, and it is the legitimate core of keyword optimization: match the naming, not the claim.
The illegitimate version — keyword stuffing, white text, a hidden block of terms in the footer — is detectable, is filtered for by every serious platform, and ends the process when a human spots it. It also fails on its own terms: appearing in a search you can't survive a five-minute conversation about wastes the interview slot you got.
The practical version is a pass over the posting for the concrete nouns — tools, frameworks, methodologies, certifications, domain terms — and a check that anything you genuinely have appears somewhere in your document using their word for it. Anything you don't have stays off.
Applicant Tracking System (ATS)
The software an employer uses to receive, store, search, and move job applications through their hiring process.
Resume tailoring
Rewriting an existing resume for one specific posting so the relevant experience is the visible experience.
Job posting
The employer's public description of a role — part specification, part marketing, and rarely a literal list of requirements.
Skills gap
The difference between what a posting asks for and what you can currently demonstrate — most of which is smaller than it looks.