Collision occurs in a hash table when two or more elements map to the same slot or index in the hash table. This can happen due to the finite number of slots available in the hash table and the potentially infinite number of elements that can be inserted into it.

Collision is an important concept to understand in hash table because it affects the efficiency and performance of hash table operations. When a collision occurs, it means that the hash function has generated the same hash value for two different elements, and both elements are supposed to be stored in the same slot.

To handle collisions, various collision resolution techniques are used. Some commonly used techniques are:

1. Separate Chaining: In separate chaining, each slot in the hash table is associated with a linked list. When a collision occurs, the collided elements are stored in the linked list associated with that slot. This way, multiple elements can be stored in the same slot without overwriting each other.

2. Open Addressing: In open addressing, when a collision occurs, the hash function is applied to the next slot in a predetermined sequence until an empty slot is found. This means that the collided element is stored in the next available slot.

3. Linear Probing: Linear probing is a type of open addressing where the next slot is searched in a linear manner. If a collision occurs at slot `i`, the next slot `i+1` is checked, and so on, until an empty slot is found.

4. Quadratic Probing: Quadratic probing is another type of open addressing where the interval between the slots checked after a collision is increased quadratically. For example, if a collision occurs at slot `i`, the next slots checked would be `i+1`, `(i+1)^2`, `(i+1)^2 + 1`, and so on.

These collision resolution techniques ensure that elements are stored and retrieved correctly from the hash table, even when collisions occur. By properly handling collisions, the efficiency and performance of hash table operations can be maintained.