What is the designated player / flex (dp/flex) in Softball?

Section 4: Players/Officials

Each team plays nine defensive players: pitcher, catcher, four infielders (first, second, third base, and shortstop), and three outfielders (left, center, right).
The batting order lists the players who will bat; it must be followed in order through the game.

The NCAA permits a Designated Player (DP) who bats for a defensive player known as the Flex. The DP occupies a spot in the batting order; the Flex plays defense and does not bat (unless entered into the DP's batting spot).
The DP and Flex give coaches flexibility to separate offensive and defensive roles, with specific rules governing when each may enter, leave, and re-enter.

Substitutes enter by being reported to the plate umpire.
Starter re-entry: A starting player who is substituted for may re-enter the game once, but must return to the same spot in the batting order.
A substitute (non-starter) who leaves the game may not return.
Pinch hitters and pinch runners are substitutions and are governed by the same re-entry rules.

Umpires: Games are worked by an umpire crew — a plate umpire plus one to three base umpires (two-, three-, or four-umpire crews). The plate umpire calls balls and strikes and has general charge of the game; base umpires rule on plays on the bases and in the outfield.
Official scorer: Keeps the official record of the game — runs, hits, errors, and the line score.
Head coach: Responsible for the conduct of the team and is the point of contact with the umpires for lineup changes, conferences, and appeals.

Each team plays nine defensive players: pitcher, catcher, four infielders (first, second, third base, and shortstop), and three outfielders (left, center, right).
The batting order lists the players who will bat; it must be followed in order through the game.

The NCAA permits a Designated Player (DP) who bats for a defensive player known as the Flex. The DP occupies a spot in the batting order; the Flex plays defense and does not bat (unless entered into the DP's batting spot).
The DP and Flex give coaches flexibility to separate offensive and defensive roles, with specific rules governing when each may enter, leave, and re-enter.

Substitutes enter by being reported to the plate umpire.
Starter re-entry: A starting player who is substituted for may re-enter the game once, but must return to the same spot in the batting order.
A substitute (non-starter) who leaves the game may not return.
Pinch hitters and pinch runners are substitutions and are governed by the same re-entry rules.

Umpires: Games are worked by an umpire crew — a plate umpire plus one to three base umpires (two-, three-, or four-umpire crews). The plate umpire calls balls and strikes and has general charge of the game; base umpires rule on plays on the bases and in the outfield.
Official scorer: Keeps the official record of the game — runs, hits, errors, and the line score.
Head coach: Responsible for the conduct of the team and is the point of contact with the umpires for lineup changes, conferences, and appeals.