Hefile or High Equipment file, refers to an e-file or equipment file (database with units and their stats) that uses high prestige costs for some units as a means of regulating the size and power of player armies.
The cost of units is important, not only in terms of the number of prestige points that must be spent to purchase them, but also because most units count against the overall cap set by a campaign designer on the value of the player's army.
The basic idea of Hefiles is twofold:
Firstly, high-end and powerful equipment would be rare and in high demand and that a General would be able to fill his entire core with nothing but 17 K18 guns, Tiger tanks and Me-262 fighters is unrealistic and unhistoric. With a Hefile, campaign designers can put the player up against a historical composition of enemy forces and the player will have a more historical composition of forces under his command.
Secondly, Hefiles forces the player to choose: quality or quantity. If the player wants high-end equipment only, he will have a very small core. If he chooses low-end equipment, he will have a enormous core, or he can go somewhere in between. This gives the player more options and removes the need for the Waffenkammer campaign design style, where the only way to challenge the player is to give the AI scores of the best equipment available, experienced and overstrengthened to the maximum. With more options that Hefiles give comes more playability and a larger diversity of campaign design.
Note that in no way does Hefiles restrict players to horse carts, 75mm guns and militia (often referred to as Horse Cart General as opposed to Panzer General - the campaign designer can still allocate enough prestige to allow the player to have high-end equipment.
Examples of low cost or Lefiles include the original SSI file and the Waffenkammer efile.