An e-Visa is an electronic visa that is linked to your passport. The entire process of obtaining an e-Visa can be done online and does not require you to visit an embassy/consulate. Once issued, you will receive an approval letter, which you usually need to present upon entry to the country you are visiting, where you will receive the visa stamp. To facilitate tourism, more and more countries are adopting the e-Visa process.
A traditional visa is where you obtain the visa sticker on your passport prior to your travel. The process usually involves applying at the appropriate embassy/consulate and some countries may require an in-person interview.