SnakeGrid is a type of Snake Projection: a projected coordinate system with grid coordinates in metres Easting/Northing. There are many SnakeGrid coordinate systems available; each one is tailored to a particular project. The most typical project it is used on is long linear engineering projects such as rail infrastructure: for the designed route the Snake projection has virtually zero scale factor distortion at track level within a corridor of approx +/- 20km.
SnakeGrids are usually defined using a '.dat' parameter file. This file will enable conversions between latitude/longitude and SnakeGrid Easting/Northing. The SnakeGrid parameter file is compatible with SnakeGrid enabled software only. This includes:
SnakeGrid PointWise. A free desktop tool for converting between
SnakeGrid E/N and lat/lon; for points and ASCII text. Requires the correct parameter file.
SnakeGrid Projector. A suite of plugins for
FME for converting between SnakeGrid E/N and lat/lon for all formats that
FME supports. Costs £500 on top of the FME licence costs. Requires the correct parameter file.
The above tools will also convert to/from SnakeGrid and UTM, US State Plane and British National Grid.
There are alternative methods of using Snake Projections using NTv2 transforms which are more generally compatible within geospatial software systems. This may or may not be available depending on which SnakeGrid you are working with.
Suggest going back to your data supplier for further information.