In essence, another term for shit or crap. Log can be used to describe something that is not enjoyable, annoying, useless, ect. Its an all encompassing word for negativity, and can be used as a noun, verb, or adjective.
"Sara is so log, she keeps yelling at me."
"Today's weather is massively loggish."
"YOUR DEFINITION IS A TOTAL LOG."
"I've really got to log, where's the washroom?"