More lighting questions/ballast/bulb combinations

[BCOrchidGuy]

I got a good deal on two 48 inch 175 watt MH units, both had some rust on the boxes the ballasts are in so I've opened one up to clean it. One is a hamilton, two 175 and the two fluorescents, it's a retrofit kit. The other is a Coralife unit, two seperate boxes, one for two MH ballasts and one for the fluorescents.
It says it's recommended for M57 or H93, what exactly does that mean.

Doug