CTE = common table expression, i.e. a WITH clause (possibly recursive) before your SELECT (or other) statement. https://learnsql.com/blog/what-is-common-table-expression/
A common table expression, or CTE, is a temporary named result set created from a simple SQL statement that can be used in subsequent SELECT, DELETE, INSERT, or UPDATE statements.
The annoying part is that certain RDMBS engines (MySQL for instance) require you to write the INSERT keyword before any CTEs.
So, your T-SQL or PGSQL query:
`with cte1 as (...) insert into ... select ... from cte1;`
becomes:
`insert into ... with cte1 as (...) select ... from cte1;`
I know the difference is minor but when you deal with many different DB engines, it is simply annoying.