help needed for guardian knitting supplement

[7oaksknitter]

Hello experienced knitters,!

I am trying to knit a hat for my daughter from the Guardian Knitting Supplement of 26th July. The following instruction appears:
slip, slip, knit slipped stitches (to increase by one stitch) I do not understand this. I haven't knitted for 30 years, and m housebound at present with a broken ankle - my daughter is determined to keep me busy. I will be grateful for your advice

Many thanks
7oaksknitter

[MerigoldinWA]

Are you sure it isn't a decrease a ssk (slip, slip, knit) is a kind of decrease an