The number of submeshes. Every material has a separate triangle list.

	function Start() {
		var mesh : Mesh = GetComponent(MeshFilter).mesh;
		Debug.Log("Submeshes: " + mesh.subMeshCount);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void Start() {
        Mesh mesh = GetComponent<MeshFilter>().mesh;
        Debug.Log("Submeshes: " + mesh.subMeshCount);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Start() as void:
		mesh as Mesh = GetComponent[of MeshFilter]().mesh
		Debug.Log(('Submeshes: ' + mesh.subMeshCount))