Functions are reusable queries or query parts. Functions can be stored as database entities (similar to, for example, tables) called stored functions. Functions can also be created in an ad-hoc fashion inside queries using a let statement through a mechanism called lambda expressions.
For more information on function invocation syntax and rules, see user-defined functions. For more information on how to create and manage stored functions, see managing functions.
For more information on working with functions in Log Analytics, see Functions in Azure Monitor log queries.