improvise, extemporise, extemporize, extemporary, off-the-cuff, extemporaneous, extempore, offhanded, spontaneous, unscripted, more...

scripted, rehearsed, planned, prepared

off script,   improvise, in a way,   improvised bit,   off-script remark,   to improvise,   good at improvising,   improv (hyph.),   improvised lines,   speak without notes,   unrehearsed comment