Watch How I Met Your Mother Season 5 Episode 1 "Definitions" online here:

http://www.tvshowslist.com/how-i-met-your-mother-season-5-episode-1-definitions/

When Marshall (Jason Segel) and the gang finds out that Barney (Neil Patrick Harris) and Robin (Cobie Smulders) are hesitant to define their relationship, Lily (Alyson Hannigan) forces them to confront their biggest fear.