Same in the US. On my paycheck there are Social Security tax, Medicare tax, State disability insurance tax, State unemployment insurance tax. If it is a mandatory deduction taken out of your paycheck to fund a government project (not the best word, but can't think of the proper word at the moment), even if you get benefits later, it's called a tax.
Social Security is a called an "insurance program" although it is completely unrelated to conventional insurance. The closest financial instrument is a Ponzi scheme, which is illegal under US law.
It is insurance in the sense that it pools the risk.
The risk here is "aging" ("Social Security" in the US only covers base retirement, whereas "Social Security" in France covers 5 risks), it only happens to be a risk that realizes 100% of the time, unlike fire insurance for instance.
