Renderer is a type of plugin for other widgets (form, grid) that displays data value in a way that is feasible for context. For instance, text in grid view will be displayed simply as text, while in form it might be input field.
Renderers might be applied to model field, with annotations.
Maslosoft Widgets comes with several bundled renderers in few flavors, usefull for different widgets.
New renderers can be added too.