"worsted" weight yarn

What does “worsted” mean? And why would I want to use something worsted vs not? Does it matter? How can I tell if my yarn is worsted? (I’m using bernat supervalue acrylic yarn) Also what does this symbol mean (ie, what do the numbers mean?) :

thanks!

Worsted is just a medium weight yarn. That’s what the number ‘4’ refers to. Other yarns that are thinner than worsted would have the numbers 3, 2, or 1 and heavier weight yarns would have a larger number on the symbol.

Different patterns call for different yarns and different needle sizes depending on what look you are after. A worsted weight yarn and a very large needle would give an open knit, whereas a worsted weight yarn and a very small needle would give you a very tight knit.

Yarn comes in different thicknesses. Worsted weight is in the middle range.

Here is a chart that shows the different weights and the stitches per inch they knit up into.