We want to go for a day and my husband wants to visit an area in downtown? Does anyone know of this area, located on waterfront??

Seaport Village most likely. It is also located near the Midway Aircraft Carrier

It may be the lamp post district.

Seaport village is nice too, you could do both

It may very well have been the Gaslamp District too.

How about just a teensy bit more to work with? What kind of an area is it?

Seaport Village is touristy shops.
Gaslamp is not on the waterfront but easy to get to from there.

The waterfront area is called the Embarcadero. That is where you will find the Midway Museum, the Star of India and the rest of the Maritime Museum.

http://www.sdmaritime.com/

www.midway.org

There are several restaurants in the area and it is all easily walkable.

As L84SKY says, Seaport Village is a cutesy, tourisy area. It is also in this general area.