google panda update was introduced in 2014 as a trial filter to filter search results. Now panda is one of the core updates of google. if you want to save your websites from the Panda Update Degrading rank system you have to keep in mind six things to avoid panda penalties.
1) poor user experience
2) Duplicate content
3) plagiarism (copying another person’s ideas, words, or work and pretending they are your own)
4) Thin Content (content which is no use of viewer)
5) keyword stuffing (You put keywords in your content excessively and unnecessarily)
6) User-generated Spam ( Aiming to increase website traffic by obtaining users unnecessarily)