`@for` is a loop inSASS that iterates through a range of numbers, allowing you to generate repetitive styles programmatically. For instance,`@for $i from 1 through 5 { .item-#{$i} { width: 20px * $i; } }` will create classes `.item-1` to `.item-5`with increasing widths. This is useful for tasks like creating grid systems or generating styles based on a numerical sequence.