Usually, rem would mean "remaining", as in, "for all remaining stitches" etc.
Yarn Over.
Slip Stitch
Probably "spaces". As in skip spaces.
How am I supposed to know I’m asking the question here
yrn is the abbreviation for 'yarn' - the material you are knitting or crocheting with
REM could mean Rapid Eye Movement, R.E.M the pop group, or it could mean the website - more information required
It means decrease, usually by crocheting stitches together.
My grandmother loves crocheting.
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Rapid Eye Movement
When a pattern refers to the "right side" of your work, they mean the side that is the front. The side that is the back will be the "wrong" side.
REM means Rapid Eye movements, a stage of sleep. I am not aware of any other meanings.