Plain meaning
Start with the shortest useful explanation before going deeper.
A vesting structure with an initial lockup period (the cliff) during which no tokens are released, followed by gradual unlocking. For example, a 4-year vest with a 1-year cliff means zero tokens unlock for the first year, then remaining tokens vest linearly over the next 3 years. The cliff ensures minimum commitment before any tokens become available and is standard for team and investor allocations.