An abstract submission is a short proposal summarizing a paper or presentation, sent for review before a program committee decides what to accept.
Usually a title, a structured summary and author details, within a word limit the organizer sets. Scientific programs often require a fixed structure such as background, methods, results and conclusions, which makes abstracts comparable across reviewers rather than a test of who writes best.
They exist so a committee can read two hundred submissions without the task becoming impossible, and so no submitter gains an advantage by writing more. Enforce them at the form rather than apologetically afterward.
Off-topic for the track, no actual findings, a pitch dressed as a talk, or submitted past the deadline. The first and third are preventable by writing a clearer call. The second is a judgment call your criteria should already cover.
An accepted abstract is the start of the work, not the end. You still need the final presentation, a bio, a headshot, consent to record and a scheduling slot. Build the chase into your timeline, because a meaningful share of accepted speakers will miss the first deadline. See abstract management software.