In short: A time bank is a community system in which people exchange services for hours: one hour of work equals one hour of work, whatever the service.
Simply put: The idea comes from the American lawyer Edgar Cahn (1980s). It gives value to people who have time and skills but little money — older people, the unemployed, students — and builds trust and connections. Its weak points: hours are not easily exchanged for euros, the system is hard to scale, and it needs a coordinator and clear rules, or it soon falls apart.
Example: Maria helps a neighbour with her shopping for an hour and gets one hour in the register. She later uses it for an hour of maths tutoring for her son — a lesson she would otherwise pay a fictional €20 for.
Watch out: A time bank is not free — it costs time and organisation. If you regularly work for "credits" or "points", that may count as income with tax consequences.
Check in your country — ask your tax authority whether regular work for time credits counts as income.
Source: Edgar Cahn, No More Throw-Away People (2000) and https://timebanks.org