Are wizards able to cast different spells or repeated spells without saying the spell incantation and just by thought and wand movement. For example when Mrs. Weasly defeated Bellatrix.
Every wizard can do it, it's just a matter of experience. I guess difficult spells are more difficult to cast without an incantation and it can be said that is safer to cast it out loud. You literally "spell" it. :)
You can find many examples of no-incantation cast spells in those two previous questions: Why does Harry always cast spells out loud? and Why were there so many spells cast in the movies without saying the words to the spell?