the chief executive department of the United States government
"The new executive branch policies will take effect immediately upon the president's arrival in Washington."
executive, executive officer
"The new exec arrived at the board meeting to present the quarterly financial report."
In plain English: An exec is short for executive, which means someone who holds an important leadership position and makes big decisions at work.
"The new exec promised to make quick decisions about the company's future."
To execute; to run.
"The system automatically executes every command stored in the script file."
The word exec is a shortened form of execute, which originally meant to carry out an action or command. It entered common usage as a clipped version of the longer term to describe performing tasks efficiently.