Vesting module provides a means of scheduled balance lock on an account. It uses the graded vesting way, which unlocks a specific amount of balance every period of time, until all balance unlocked.
The schedule of a vesting is described by data structure VestingSchedule: from the block number of start, for every period amount of blocks, per_period amount of balance would unlocked, until number of periods period_count reached. Note in vesting schedules, time is measured by block number. All VestingSchedules under an account could be queried in chain state.