A convertible car seat is a type of car seat that can be adjusted to fit babies and young children as they grow. It can be used in both rear-facing and forward-facing positions, providing safety and comfort during car rides. Full definition
While in general, it is true that infant carseats do fit newborns better than many convertible carseats, more and more convertible seats these days are just as well - designed to fit small infants. (ecochildsplay.com)
Convertible Carseat Maxi - Cosi Pria 70 Picking the right car seat can be an overwhelming experience. (mommasociety.com)
For example research convertible carseats, my Daughter is 16 months old weighing 15.5 lbs and is in a Britax Advocate and Marathon Rear facing, and I plan on keeping her RF until she reaches the weight limit, which is I believe 40 lbs. (babycenter.com)