The extracellular matrix is a netlike mixture of polysaccharides and proteins that surround a cell. It provides a molecular scaffolding around the cell and helps the cell attach to a surface on which it can grow. The proteoglycans (proteins bound to sugars) in the matrix create a sort of gel that provides routes through which hormones, nutrients, and other chemicals can move in and out of the cell.
The composition of this matrix in cancerous tissue is drastically different from the matrix in normal tissue and, partly because of this, the composition is thought to influence the regulation of cell growth, division, and differentiation.
The extracellular matrix is also an important component of the fluid that surrounds and cushions joints.
From the science dictionary at http://biotech.icmb.utexas.edu/