A traveling looper is a looper who rarely or never loops into their home universe, or doesn't have one to begin with. This mainly happens because of glitches, caused by accidents involving The Hub or Yggdrasil while the looper was trying to return to their home loop. Another factor is loss of loops, once again caused by glitches or more sinister forces, and often can't be resolved without lots of hard work from the Administrators and the individual; if it can be resolved at all.
Most traveling loopers are pitied by other loopers and generally have a more lost or short-tempered persona because of constant relocation.
It's also thought that if an Anchor becomes a traveling looper, the entire loop system they're from shuts down. Luckily this hasn't happened, and hopefully never will.