Probably hit E key or V key. which can turn on filter.
F5 to set it to ON
F6 to set it to OFF
You can also use the Filter toolbar to set it on/off plus pick entities in case you need to use filter for selection. For e.g. if you want to pick edges only, then set the filter to ON and select the edge filter from the toolbar (or the shortcut for it. Then your cursor would only be able to pick edges.