PRISMA stands for: Preferred Reporting Items for Systematic Reviews and Meta-Analyses. PRISMA is a standard that gives guidance for the reporting of Systematic Reviews.
You can read more about the most updated PRISMA standards here:
Page, M. J., McKenzie, J. E., Bossuyt, P. M., Boutron, I., Hoffmann, T. C., Mulrow, C. D., Shamseer, L., Tetzlaff, J. M., Akl, E. A., Brennan, S. E., Chou, R., Glanville, J., Grimshaw, J. M., Hróbjartsson, A., Lalu, M. M., Li, T., Loder, E. W., Mayo-Wilson, E., McDonald, S., McGuinness, L. A., ... Moher, D. (2021). The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. Journal of Clinical Epidemiology, 134, 178–189. https://doi.org/10.1016/j.jclinepi.2021.03.001
The PRISMA Statement issues a minimum set of items for detailing a Systematic Review. It comprises of a checklist of items to include in the report, and a flow diagram. The PRISMA statement is periodically revised, however the latest version of the PRISMA statement and the checklist will always be made available on the PRISMA Statement website.
The flow diagram shows the flow of information through the different stages of a Systematic Review. It maps out the number of records identified, included and excluded, and the reasons for exclusions. Different flow diagram templates are available depending on the type of review (new or updated) and sources used to search for studies.
There are several extensions of the PRISMA Statement for reporting of different types or parts of systematic reviews. For example PRISMA-P for developing a research protocol and PRISMA-S for reporting on database searches.
The various extensions are available here.