means the hay ford, as in a ford used mainly at hay-making time.
The 'lower' differentiates this ford from the one at Upper Heyford,
a short distance downsream.
travel by road to Lower Heyford, take the M40 and exit at Junction
10 (one hour and five minutes from London approx, 55 minutes from
Birmingham approx). Take the B430 to Middleton Stoney, turn right
at the traffic lights there on to the B4030. Carry straight on to
Lower Heyford. There is a crossroads, and if you turn left you will
reach the railway station and canal boat centre, or carry straight
over the crossroads into Freehold Street which winds down to the
Lower Heyford Market Square.