from clause

from keyword is defined as

from-clause ::= from itemName in srcExpr

MSDN says:

A query expression must begin with a from clause. Additionally, a query expression can contain sub-queries, which also begin with a from clause. The from clause specifies the following:

• The data source on which the query or sub-query will be run.
• A local range variable that represents each element in the source sequence.

Both the range variable and the data source are strongly typed. The data source referenced in the from clause must have a type of IEnumerable, IEnumerable<T>, or a derived type such as IQueryable.

Or it can be replaced with iteration statement foreach, where func is delegate:

foreach(var itemName in srcExpr){
   func(itemName);
}