In JavaScript, a loop is a control structure that allows for the repeated execution of a block of code until a specified condition is met. Loops are fundamental for automating repetitive tasks and processing collections of data efficiently, avoiding the need to write the same code multiple times.

There are several types of loops in JavaScript:

1. for loop

Used when the number of repetitions is known.
 

2. while loop

Repeats while a condition is true.

3. do...while loop

Runs the code at least once, then repeats while the condition is true.

4. for...of loop (used for arrays)

5. for...in loop (used for objects)