In this paper we introduce a parameter si1" class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002437951630413X&_mathId=si1.gif&_user=111111111&_pii=S002437951630413X&_rdoc=1&_issn=00243795&md5=b7e3358fddb55fe03659090b7a8583bb" title="Click to view the MathML source">Mm(G)class="mathContainer hidden">class="mathCode">, defined as the maximum over the minimal multiplicities of eigenvalues among all symmetric matrices corresponding to a graph G . We develop basic properties of si1" class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002437951630413X&_mathId=si1.gif&_user=111111111&_pii=S002437951630413X&_rdoc=1&_issn=00243795&md5=b7e3358fddb55fe03659090b7a8583bb" title="Click to view the MathML source">Mm(G)class="mathContainer hidden">class="mathCode"> and compute it for several families of graphs.