It is a masculine singular noun, meaning it refers to a specific kiss that has already been mentioned or is understood in the context of the conversation.
Here are some examples of how it can be used:
* "Ese beso fue mágico." (That kiss was magical.)
* "¿Recuerdas ese beso en la playa?" (Do you remember that kiss on the beach?)
* "No puedo olvidar ese beso que me diste." (I can't forget that kiss you gave me.)