Meaning of m2 in the symbol for an isotope of an element
As per this Wikipedia page on isotopes:


  The letter $m$ is sometimes appended after the mass number to indicate a nuclear isomer, a metastable or energetically-excited nuclear state (as opposed to the lowest-energy ground state), for example $\ce{^{180\mathrm{m}}_73Ta}$ (tantalum-180m).


Note that the lower subscript to the left of the chemical symbol is the atomic number of the element (in the example above, 73 is the atomic number for tantalum) and is omitted in your example.