Yes, these are two separate products for two distinct applications. These terms are NOT synonymous! A gas fireplace insert is to be slid into an existing wood burning fireplace. A gas fireplace is designed to be built into a framed wall. This is done during construction or a remodeling project. An insulated shell around the gas firebox provides protection against overheating any wooden framing members.
Gas inserts usually come in a few sizes, small, medium and large depending on the dimensions of the wood-burning firebox. But a gas fireplace can be a traditional or linear model. Maybe a see through or two-sided corner model for that special spot in the living or dining room. There are literally dozens of sizes available when it comes to a gas fireplace. And with venting options horizontally through a sidewall or vertically through the roof, a gas fireplace could be installed in several locations in your home. An insert to upgrade your existing wood burning fireplace is vented vertically through the existing fireplace chimney.