Lakeshore Avenue is a street that goes up and down the east side of Lake Merritt and then goes up through the middle of the Lakeshore neighborhood up a bit into the hills.
If you hear someone say "I'm going to Lakeshore Avenue" or "Do you want to get pizza on Lakeshore?" they are usually referring to the commercial strip portion of Lakeshore that goes from Highway 580 up until it gets a bit hilly. This is usually a busy strip with restaurants, stores, bars, people, etc. It gets extra busy on Saturday mornings and afternoons when the Grand Lake Farmers' Market is going on.