What is a Collection in MongoDB?

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A collection is MongoDB's equivalent of a table : a group of documents inside a database. No fixed schema — documents in the same collection can have different fields. Created lazily — the first insert creates it; no CREATE TABLE step required. Indexes per collection — including the automatic unique index on _id . Collection options — capped (fixed size), TTL (auto-expire), schema validation (JSON Schema rules). Sharded — distributed across shards based on a shard key. Collections are schema-flexible (not schema-less — you can enforce schemas with validation). Know capped collections (fixed-size, FIFO) and time series collections (IoT, metrics). Collections are created implicitly on first insert — no CREATE TABLE needed.