In California, a highway usually has only 1-2 lanes and doesn't necessarily have off-ramps. A highway's speed limit is subject to change if it's passing through a town or sharp bends. Highways can have that dashed yellow line that allows you to briefly move into the oncoming traffic lane to pass.
Freeways are much bigger and are either interstates, or state freeways in more urban areas. Freeway's are usually a flat 55-65 speed "limit" unless you have a trailer. It's a pretty distinct difference.