Lightning Web Component: This is a new programming model for developing the lightning components. It uses the W3C web standard for building the component that makes it better, robust, and powerful/fast. LWC is lightning weight framework based on the web standard, it uses custom elements, templates, shadow DOM, events, modules and others that are available in the latest ECMAScript.
LWC uses API based on the UI-API for better performance, that makes it less Apex to write and calling server side is a less painful experience.
LWC is combinations of Aura Framework and web components, so the developer who has experience in web component can get into faster and of course, the developer who worked with the Aura Framework already knows the standard components and syntax. If you already worked with Aura Framework then you just need to translate the old syntax (Aura) to new (LWC) and believe me this is very easy. 🙂
Below are very useful Trailhead (Module) links that you can follow to learn LWC: Start learning in the order links are given that will help you to understand the things better.