Burak Yavuz, et al, explain the concept of schema enforcement with Databricks Delta Lake:
Schema enforcement, also known as schema validation, is a safeguard in Delta Lake that ensures data quality by rejecting writes to a table that do not match the table’s schema. Like the front desk manager at a busy restaurant that only accepts reservations, it checks to see whether each column in data inserted into the table is on its list of expected columns (in other words, whether each one has a “reservation”), and rejects any writes with columns that aren’t on the list.
Something something “relational database” something something. They also walk us through some examples in a Databricks notebook, so check that out.