My character jumps infinitely, even when in mid-air

I'm making a 2D platformer but I run into a bit of a problem, if you press the jump key repeatedly when the character is in mid-air, it will keep jumping. I only want the character to jump when it's making contact with the floor or a wall. Here's my code:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerScript : MonoBehaviour {
         
     public float playerSpeed = 5.0f;
 
     public float glideSpeed = 2.5f;
     
 
     // Use this for initialization
     void Start () {
 
         //PlayerSpawnPoint
         transform.position = new Vector3(0, 0, 0);
 
         Physics.gravity = new Vector3(0, -1.0F, 0);
         
     }
     
     // Update is called once per frame
     void Update () {
 
     //Player Movement, left and right using arrow keys
         transform.Translate(Vector3.right * Input.GetAxis("Horizontal") * playerSpeed * Time.deltaTime);
 
         transform.Translate (Vector3.up * Input.GetAxis("Jump") * playerSpeed * Time.deltaTime);  
 
 
     }
 }