Type of cyst that contains an epithelial lined cavity that is open towards the  root canal of the aﬀected tooth is known as:
Periapical pocket cyst:

The cyst contains an epithelial-lined cavity that is open towards the root canal of the aﬀected tooth. 
It was originally designated as bay cyst and is now redesignated as the periapical pocket cyst.
The periapical pocket cyst is probably initiated by the accumulation of neutrophils around the apical foramen in response to microbial bioﬁlm present in the apical portion of the root canal. 
This forms a microabscess that gets enclosed by the proliferating epithelium, forming a collar with epithelial attachment on contacting the root tip. 

Textbook of Endodontics Nisha GARG 3rd ED
Periapical true cyst
Periapical pocket cyst
Periapical pseudocyst
Degenerative cyst