What is the difference between a Mobile Hotspot and a 4G LTE Router ?

A 3G/4G/LTE Wireless Router is a NAT router with module to connect to a mobile network. It usually includes a slot for a SIM card, and it can serve as an access point to multiple WiFi enabled client devices, such as laptops, PCs, tablets, smartphones, etc. It usually has LAN ports for connecting wired clients, and it can also be referred to as a 3G/4G WiFi Router. 4G variants usually have two external antenna ports for MIMO transmissions. Mobile routers are designed to remain mostly stationary at the customer premises and provide internet access via mobile networks.

In contrast, a 3G/4G/LTE Mobile Hotspot is a much smaller variant (a.k.a. LTE MiFi, or 4G Mobile WiFi) designed to be easily transported and to provide internet access on the go. Hotspots are portable travel routers that allow for mobile network connectivity and a very small number of clients, most of them have no LAN ports for wired client devices. Some may have a built-in battery for internet access where power is not readily available.