I am looking online for homes for sale. One of the houses I really like say is has a roughed in master bath, what does this mean?

It means its ready for the accountrements, such as a bath tub sink toilet. Not quite done yet but ready to be.

What rough in means is simply that they have the piping for a bathroom , which includes supply lines for your sink and toilet and drain lines. Mostlikely there is no sheetrock installed and there could be some insulation in the walls already, that's about it