Would this be a short but generally correct answer ?
LINQ to SQL should really be called LINQ to T-SQL because "LINQ to SQL" code just gets translated to T-SQL and then it runs in MSSQL (Only) !!!
LINQ to Objects actually run the SQL thats coded. And it only works on objects - data in code (or even variables created in code with var or anything else that takes up residence in memory),
or, after any data is read from any database and turned into an object that exists, where ? ... IN-MEMORY !
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