Yarn is a descriptive term for any spun thread. Yarn for crochet can be natural wool, but so can acrylic, polyester, bamboo or cotton.
Choosing the Right Yarn
How to Match Crochet Hook Size and Yarn Weight
Yarn Weight Chart & Guide to Yarn Sizes/Types
The BEST Yarn for Crochet Beginners: A COMPLETE Guide - sigoni macaroni
How to Match Crochet Hook Size and Yarn Weight
Understanding Crochet Hook Sizes & Yarn Weights
Yarn Weight Chart & Guide to Yarn Sizes/Types
Crochet Hook Sizes and Yarn Weights - Dora Does
50+ Free Crochet Worsted Weight Yarn Patterns - Simply Hooked by Janet
What's the right hook size for crocheting amigurumi?
Understanding Crochet Hook Sizes & Yarn Weights
Yarn Weight Chart + Recommended Yarns for Each Weight
Yarn Weights – One and Two Company Crochet Blog
Ceralena Sweater Crochet Pattern - Electronic Download
Solved: Does Crochet Hook Size Matter?