This is simply the orchid's parents: So, (Dendrobium speciosum x dendrobium gracilicaule) are crossed with Dendrobium Specio-kingianum (Den. kingianum x Den. speciosum). The first cross is yet unnamed the second one Dendrobium Specio-kingianum is the named cross of Dend. kingianum crossed with Dend. speciosum). The "M" is the clonal name given to this cross.