The word rakhi means ‘band’. So, this festival is called Rakhi because during the festival it is traditional for a sibling to tie a band or rakhi around the wrist of their other sibling in order to symbolize the bond that binds them.
In general, Rakhi festival or Raksha Bandhan is a festival that celebrates brotherhood, sisterhood and the bonds that bind us to other who (though we are not biologically related to them) feel like our siblings.
At first sisters would tie the rakhi around their brother’s wrist, but now anyone can perform this on anyone else - and close friends do it too. A rakhi will usually be red and gold.
Rakhi festival is another name for Raksha Bandhan Festival. Many people use the form Rakhi as the name of this festival because that name is more popular in the region where they live. Others call the festival Rakhi because this name is a shorter form than Raksha Bandhan.
Edited.