Leaflet is a widely used open source JavaScript library used to build web mapping applications. First released in 2011, it supports most mobile and desktop platforms, supporting HTML5 and CSS3.
Along with OpenLayers, and the Google Maps API, it is one of the most popular JavaScript mapping libraries and is used by major web sites such as FourSquare, Pinterest and Flickr - wikipedia 
Leaflet allows developers without a GIS background to very easily display tiled web maps hosted on a public server, with optional tiled overlays. It can load feature data from GeoJSON files, style it and create interactive layers, such as markers with popups when clicked.
Leaflet supports Web Map Service (WMS) layers, GeoJSON layers, Vector (Vector graphics) layers and Tile layers natively. Many other types of layers are supported via plugins (Plug-in (computing)) - wikipedia
Like other web map libraries, the basic display model implemented by Leaflet is one basemap, plus zero or more translucent overlays, with zero or more vector objects displayed on top.
# Use
A typical use of Leaflet involves binding a Leaflet "map" element to an HTML element such as a div. Layers and markers are then added to the map element.
// create a map in the "map" div, set the view to a given place and zoom var map = L.map('map').setView([51.505, -0.09], 13); // add an OpenStreetMap tile layer L.tileLayer('http://{s}.tile.osm.org/{z}/{x}/{y}.png', { attribution: '&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors' }).addTo(map);
The Leaflet library itself is accessible through the variable L.
# Comparison with other libraries
Leaflet is directly comparable with OpenLayers, as both are open source, client-side only JavaScript libraries.
The library as a whole is much smaller, around 7,000 lines of code compared to 230,000 as of 2015. It has a smaller code footprint than OpenLayers (around 123 KB vs 423 KB due partly to its modular structure.
The code base is newer, and takes advantage of recent features of JavaScript, plus HTML5 and CSS3. However, Leaflet lacks features OpenLayers supports, such as Web Feature Service (WFS) and native support for projections other than Google - Web Mercator.
It is also comparable to the proprietary, closed source Google Maps API and Bing Maps API, both of which incorporate a significant server-side component to provide services such as geocoding, routing, search and integration with features such as Google Earth (Google Earth).
Google Maps API provides speed and simplicity, but is not flexible, and can only be used to access Google Maps services. The new DataLayer part of Google's API does allow external data sources to be displayed, however.
# See also * Features