Gi means uniform, (long sleeve canvass top that is reinforced and triple stitched so it does not tear or rip, and somewhat lighter canvass pants with a gusset in them)  The difference is that some chokes, joint locks, holds, and restraints rely on using your opponent's uniform or your own to apply them. Not only that but it also prevents slippage and makes it harder for opponents to slip out of those types of techniques. That's why you would sometimes see Japanese fighters in Pride wear gi tops.

Obi is the name for the belt or sash that is used to tie a kimono. It is worn around the waist underneath the hakama. Depending on gender, age, season and clothing style it is long and decorated with embroidery and other methods. The obi is often as expensive as the kimono itself. It is usually made of bleached cotton. It is a Japanese garment.
 

Tabi or also called tabi boots are call odori.                           Odori tabi socks are made of  cotton and have a vinyl sole  bottom with clasps on the back.    

                                                                                      The Term tabi boot was coined by westerners for the sock goes past the ankle and resemble boots. Odori tabi socks are purchased to the exact fit of the persons foot. The tabi are popular among traditional japanese dancers and theater artists. The vinyl sole bottom of the tabi protects their feet since japanese shoes are not normally worn during performances. However, the odori tabi socks are difficult to maintain because they must be hand washed and line dried so they will not shrink