I'm not who you're replying to but strictly speaking "republic" simply means a government based on rules, technically every democracy is a type of republic. But

I'm not who you're replying to but strictly speaking "republic" simply means a government based on rules, technically every democracy is a type of republic. But the US system is a republic very different from a democracy, with democratic institutions but also rules and institutions that cannot be changed democratically and many non democratic processes. To understand how the US government works it is very similar to the UK under Oliver Cromwell prior to the attempted creation of the third house, it was basically modeled after that period of UK government.