What is the slime and smell coming from my basement walls?

Mold? Call someone to get it checked and addressed. Google slime mold and mold removal near you.

What are the walls made of, Concrete, Block? Where are you located?

Mold would require something wet and organic to grow on. If you have a wet spot on the foundation wall near where the sewer line passes through then the line right outside the house may be blocked by roots or may have a crack. On my first house I noticed an odor in the house and the sump pump in the crawlspace kept turning on even when we didn't have any rain. It turned out that the ABS sewer pipe under the house connected to terra cotta pipe at the footing, and the roots of the shrubs that I had planted outside had grown into the joints of the terra cotta pipe and blocked it, so sewage was backing up into the crawlspace.