Begining Intermediate Knitter

I'm making a baby sweater with a collar. Never made one with a collar. Little confused by collar/border instructions. Can you help

Here is how they read:

At lower edge of right front pickup and knit 6 sts evenly along rib, 42 sts evenly along straight edge, 30 sts evenly along shaped edge, 24 sts from 20 cast off sts at back of neck, 30 sts evenly along shaped edge, 42 sts evenly along straight edge and 6 sts evenly along rib. 180 sts.

Not sure what is mean't by the cast off instruction.

Thank you for your help.

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