¨Sin¨ is a Spanish word that means lack of something. This word also means in absence or without the presence of someone or something. It is usually used as well for something that is not included, an example would be: This is the price without taxes. In Spanish is very common when there is a verb in infinitive, ¨Sin¨ means ¨No¨ with its participle or gerund, an example would be: I left without eating.

The word ´´pijama´´ is also a Spanish word, it refers to sleepwear. So the correct translation in English of ¨Sin Pijama¨ is without pajamas or no pajamas.
This is also the name of a reggaeton song from Becky G and Natti Natasha, in this context ¨sin pijama¨ song or without pajamas refers to a proposal to stay at home without worries, a kinky night without clothes because they won’t sleep so there is no need of pajamas.
Basically the singers are making a proposal for a guy in order to make him to invite them to his place. They said a lot of times that if the guy calls them, they will go together and expend all night without clothes. The girls said a lot of times they will lose control and be nice with him at bed. Also they will smoke weed all over the night with no pajamas.
Of course the meaning of the song can be used as a kinky message for someone who wants to invite you to his or her place. The lyrics start as a description of two young girls having a pijama party and sending the event to the male singer, Prince Roy, at the beginning of the song.
At the end the girls just woke up and realize the guy who they called at the beginning is calling them back. Therefore all the video was just an illusion because the singers were having a real pijama party with a lot of their girlfriends and no males. All the song was like an idea how it will be if the guy call them and invite them to his place instead of the boring pajamas party they had.
It is suppose than Prince Royce saw all the video and call them back at the end of the video accepting the proposal, but the girls are just in a normal pijama party with mask and surrounding by a lot of their girlfriends.