Tokenomics (token economics) describes how a token's supply and incentives are designed: how many tokens exist or will ever exist, how they're distributed (to the team, investors, the community), how new tokens are issued over time, and what the token is actually needed for within its project.
Understanding a project's tokenomics is a core part of research before relying on or holding any token — a large allocation to the founding team with little lock-up, for example, is a very different risk profile from a token distributed broadly with long vesting schedules.