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Power Query M formula language: each expression

An each expression defines an anonymous function with one parameter whose name is the underscore (_).
each [XYZ] is equal to _[XYZ] which is equal to (_) => _[XYZ].
The following example evaluates to the list { 123457, 123457 }. 
let
   incr     = each   _ + 1,
   incr_    = (_) => _ + 1,  // same thing as above
   get_fld  = each   _[FLD],
   get_fld_ = (_) => _[FLD], // same thing as above
   REC      = [
     ABC = "abcdef",
     FLD =  123456
   ]
in
  {
     incr (get_fld (REC)),
     incr_(get_fld_(REC))
  }
Github repository about-Power-Query-Formula-M, path: /language/expressions/each/intro.M
Because [X] is a shorthand for _[X], an each expression that accesses a record-field can further be abbreviated like so (which evaluates to "Hello world"): 
let
   get_fld = each [txt],
   REC     = [
                num =  42,
                txt = "Hello world"
             ]
in
   get_fld(REC)
Github repository about-Power-Query-Formula-M, path: /language/expressions/each/record-underscore.M

Example with List.Select

The «power» of an each expression shines for example when using together with List.Select. List.Select is a function that finds elements of a list that possess a certain characteristics. This characteristics is evaluated with the second parameter of List.Select which expects a function with one parameter. If this function returns true, the element is retained in the resulting list, otherwise, it is discarded: 
let
    L      = {
               [ a = 1, b = 7, c = "A" ],
               [ a = 3, b = 6, c = "B" ],
               [ a = 9, b = 7, c = "C" ],
               [ a = 8, b = 2, c = "D" ],
               [ a = 2, b = 4, c = "E" ],
               [ a = 4, b = 5, c = "F" ]
             },

    a_gt_b = List.Select(
               L,
               each [a] > [b]
             )
in
    Table.FromList(
        a_gt_b,
        Record.FieldValues,          // Apply this function on each element in a_gt_b: it turns the record into a list
      { "col a", "col b", "col c" }  // Name the columns
   )
Github repository about-Power-Query-Formula-M, path: /language/expressions/each/List.Select.M
When evaluated in Excel, for example with this VBA code, this formula evaluates to:

Index