The prefix "per-" appears in the names of many compounds, such as in perchlorate, persulfate, peroxide. What does it mean?
Per- can mean a number of different things, depending on the context. It can mean that there is a peroxi bond(oxygen-oxygen bond) in the system, persulfate is a good example of this.
More generally it tends to mean that the compound is the most completely altered product of a certain(possibly hypothetical) reaction. For example perchlorates and permanganates are the most completely oxygenated compounds of chlorine and manganese, respectively. This also describes another common use of per-, perhalogenated compounds. In that context, it usually means that all hydrogens present in the parent compound, that were bonded to a carbon, have been replaced with a halogen, for example perfluoroethylene (C2F4, also known as tetrafluoroethylene, the monomer of Teflon(PTFE))