Pigeon toed. It just means that the horse is not breaking over dead centre of his hoof this then means that the angle of the hoof walls may vary on the inside and outside of the hoof as one is being worn away quicker than the other.
My mare was slightly pigeon toed and the farrier sorted it, although she spent all of last year with no shoes, out to grass with her foal so her feet weren't as straight when we came to put shoes back on her. she was never lame in front.
Supreme Rock, Pippa Funnels top event horse a few years back, was slightly pigeon toed and it didn't stop him winning Badminton and going to the Olympics.
It isn't very much to worry about unless it is extreme which is when it can cause strain on the joints etc, but your vet and farrier can advise you on this.