An ooze is an amorphous or mutable creature, usually mindless. Typical forms for these creatures include living puddles and blobs of gelatin.
Since their bodies tend to have no set form, they are often immune to critical hits, knockdown, paralysis, and sneak attacks. As mindless creatures, they are generally immune to mind-affecting spells. The substance from which they are made tends to give them 100% immunity to electrical damage and poison. However, these defenses may vary from ooze to ooze, and are more a guideline for custom content creators than for the few oozes defined by BioWare.
This racial type was added with the Hordes of the Underdark expansion. As a consequence (and probably an oversight), this race is not an option for a ranger's (or Harper scout's) favored enemy.
See also: Category:Oozes