Looks like any long-ignored 4runner I've seen. It could mean something (minor) or could mean nothing. Clean it up, THOROUGHLY, and monitor. My personal guess is that you're witnessing the leavings of the most common of 4runner oil leaks, the valve cover gaskets. Poke around with some light and see if the oil trail goes up to the firewall side of the engine/valve covers...

Since you've seen no major oil loss, and it runs/drives fine, no reason to get anxious. If you Really want to investigate, once you have the engine de-greased and cleaned (I prefer a cheap toilet scrubber, the kind with the metal wire loop, you can bend it into all sorts of great positions for cleaning), oh and dry, you can spray on anything that'll leave a powder. Think deodorant or athletes foot spray. I haven't needed to do this for a bit over a decade, but it was still available back then... anyway, you dust EVERYTHING with that powder, go for a ~60 mile drive and then look for brown streaks in the white powder. Should 100% pinpoint your leak (or leaks, if you're lucky like I was ~ both sides valve cover gaskets, might have been cam seals).

Anyway, relax and have a homebrew.... er, wrong forum. Relax, its nothing Major, just a warning that something needs to be addressed.