The fraction of the distance specified to the physics query before it detected a Collider2D.
When a physics query is used, it has a start position and an explicit end position or a direction and distance. The fraction is a value in the range of 0 and 1 which is a representation of the returned RaycastHit2D.distance result (see code example).
If the physics query does not allow specifying an explicit end position or it has a default distance of infinity then the fraction is identical to the returned RaycastHit2D.distance and therefore will not be in the range of 0 and 1.
Additional resources: RaycastHit2D.distance.
using UnityEngine;
public class ExampleClass : MonoBehaviour { public Vector2 direction;
void Update() { // Cast a ray in the specified direction up to 10 world units away. RaycastHit2D hit = Physics2D.Raycast(transform.position, direction, 10f);
// If we hit something then indicate if it was less-than or greater-than halfway of the physics query. if (hit) { if (hit.fraction < 0.5f) Debug.Log("Hit something before halfway!"); else Debug.Log("Hit something after halfway!"); } } }