Rhotacism

Rhotacism refers to several phenomena related to the usage of the consonant r (whether as an alveolar tap, alveolar trill, or the rarer uvular trill):

• the excessive or idiosyncratic use of the r;
• the inability to pronounce (or difficulty in pronouncing) r.
• the conversion of another consonant into r.

The term comes from the Greek letter rho, denoting "r".