1) Post-coital remains or drippings on sheets, towels, clothing, etc. Gender unspecific term for any of the following: dick cheese, penis snot, pussy loogies, condom smear etc
2) Related to verb: to strap meaning to have sex
3) Related to participle: strapping
Strappings are much harder to hide on blue sheets.
JWZ was using his buddy's apartment and found strappings on the sheets and pillows. As payback he left an upper decker.