The term hybrid open access refers to the possibility that (especially large) publishers offer authors to make the individual article open access in an otherwise subscription-based journal.

The publishers are usually charging author fees (APC - Article Processing Charges) that are very high. Here are some examples:

• Elsevier: USD 0-5,000 depending on journal
• SAGE (via the platform SAGE Choice): USD 3,000
• Springer (via the platform Open Choice): EUR 2,200
• Taylor & Francis (via the platform Open Select): EUR 2,150
• Wiley (via the platform OnlineOpen):  EUR 1,250-4,700 depending on journal

If you have received money from a research funder which has an open access policy the fee is covered by that.

Further reading:

Björk B. (2017). Growth of hybrid open access, 2009–2016. PeerJ 5:e3878 https://doi.org/10.7717/peerj.3878

Boyes, P. & Kingsley, D. (2016). Hybrid open access – an analysis. Retrieved October 12, 2017, from https://unlockingresearch-blog.lib.cam.ac.uk/?p=969