The important factor with dominants and submissives is that the submissive grants the dominant long-term authority to engage them (the submissive) in an agreed range of activities without seeking permission on each occasion.
Others see master and slave to be a step further along in regards to authority from that which dominants and submissives practice. Where a submissive will hand over authority over their involvement in a limited range of activities for as long as it basically suits them, a slave will hand over authority without such specific limits.
In practice this means a much more intrusive involvement of the master in the life of the slave, not just when engaging in specific BDSM activities. For example, the master may decide how the slave dresses, what the slave does in their non-BDSM time, and---of course---when any BDSM activities are done.
Thus, the experience of power is much more wide-ranging for the master.