contract players usually have a specific number of days they are guaranteed per week. might be 2, 3, maybe 1. If they don't appear for a while, then we will see them 2 or 3 times in one week, over their usual guarantee to make up for it.
Recurring players are not on contract, thus are paid only for their appearances. So, they can get used for several weeks, and then not for a couple months. (Justin, Adrienne, Lucas, Victor, all examples). Really short term may have story but only appear a few days, are gone. Like Anna, Carrie & Austin recently, Jade's dad, Dr. Lee.
Day players are the back ground people, walking in the square, sitting at adjoining restaurant tables, filling the back pews in a church. Usually no lines, or less than 5.
I don't mind Jen & Eric being really good friends, even a bit of time as Friends with benefits. Just not long term. I don't think he is the guy for Jen, although her experience is helping Jack get over his self loathing is helping her do the same for Eric.