Step 1: Define ambidentate ligand.
An ambidentate ligand is a unidentate ligand that possesses two different donor atoms through either of which it can coordinate to the central metal ion, but it bonds through only one atom at a time. Example: thiocyanate $SCN^-$ can bind via S (forming $M$-$SCN$, thiocyanato) or via N (forming $M$-$NCS$, isothiocyanato).
Step 2: Give another example for clarity.
Nitrite ion $NO_2^-$ can coordinate through oxygen (giving nitrito $M$-$ONO$) or through nitrogen (giving nitro $M$-$NO_2$), making it a classic ambidentate ligand.
Step 3: Define crystal field splitting energy.
Crystal field splitting energy ($\Delta_o$ in octahedral complexes) is the energy difference between the two sets of d-orbitals that result when the five originally degenerate d-orbitals of the central metal ion split under the electrostatic field of approaching ligands. In an octahedral field, the lower $t_{2g}$ set (3 orbitals) and the higher $e_g$ set (2 orbitals) are separated by $\Delta_o$.
Step 4: Significance.
The magnitude of $\Delta_o$ depends on the nature of the ligand (strong-field ligands give large $\Delta_o$) and determines whether the complex is high-spin or low-spin.