What does Starching mean?

The process by which starch is applied to stiffen textile fabrics in laundering.

Heddels explains Starching

Starching, a process used to increase the crispness of fabrics, dates back to the sixteenth century when it was used to stiffen the collars and ruffles that were in fashion at the time.

Starch can either be added in while washing or applied directly to dry fabric before ironing. With raw denim, starching is sometimes used during the breaking-in process to help the jeans retain their crispness and allow the creases to set.

Additional Resources

The end-result of starching:

Raw Denim Term - Starching