I'd never heard of this name, but a quick check reveals that it's a genuine Lancashire surname, though a rare one. There were 202 people of this name at the 1881 Census, and 201 in 1998, so it isn't gaining ground. The stronghold of the name is Preston, Lancashire, and it must be a place-name. Perhaps a lost one, as it isn't listed in the Gazetteer of Great Britain. At a guess I'd say it means the HALH, or piece of land belonging to a man called Esmond, or the Norse Asmund, the H being a later addition.