Master

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Whether this image is of a master and slave is not something we can tell just from a photo. Mastery and slavery have to do with how authority is exercised between two people and it doesn't show up in a photo. She does seem to be having a good time, though!

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.

Confusingly, many people consider the terms master and slave to be equal to dominant and submissive, respectively.

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.