what is Unexpected token??

“Assets/FPSScripts/PlayerMovementScript.js(34,10): BCE0043: Unexpected token: grounded.”

   var walkAcceleration : float = 5;
var cameraObject : GameObject;
var maxWalkspeed : float = 20;

@HideInInspector
var horizontalMovement : Vector2;

var jumpVelocity : float = 20;
@HideInInspector
var  grounded : boolean = false;
var maxSlope : float = 60;
function Update () 
{
   horizontalMovement = Vector2(rigidbody.velocity.x,rigidbody.velocity.z);
   if (horizontalMovement.magnitude > maxWalkspeed)
   {
      horizontalMovement = horizontalMovement.normalized;
      horizontalMovement *= maxWalkspeed;
   }
   rigidbody.velocity.x = horizontalMovement.x;
   rigidbody.velocity.z = horizontalMovement.y;
   
   transform.rotation = Quaternion.Euler(0,cameraObject.GetComponent(MauseLookScript).currentYRotation,0);
   rigidbody.AddRelativeForce(Input.GetAxis("Horizontal") * walkAcceleration,0,Input.GetAxis("Vertical") * walkAcceleration);
   
   if(Input.GetButtonDown("Jump") && grounded)
     rigidbody.AddForce(0,jumpVelocity,0);
}

function onCollisionStay (Collision : Collision)
{
   for(var contact : ContactPoint in collision.contacts)
   {
      if(Vector3.Angle(contact.normal,Vector3.up) < maxSlope)
         grounded : true;
   }
}

you want grounded = true not grounded : true

Also the function is OnCollisionStay with a capital O.