There is plenty of jargon around to help make something that might already be overwhelming, just that little bit more confusing. So here is some jargon busting to try and help make things clearer for you.
Car seats are classified according to weight and height. That is because the crash dummies used for testing don't have ages but do have different weights and heights. This is the information you need about your child before you go car seat shopping. Of course if you come to us we can help you with that.
Group 0+ - these car seats are known as infant carriers. These are the ones with a handle and have an optional isofix base. These car seats are for newborns and have a weight limit of 13Kg and a height limit ranging from 75 to 85cm depending on the seat. This is approximately suitable for the first 12-18 months.
Group 0+/1 - These go from newborn upto 18-20Kg and have a height limit of 105cm. These seats stay fixed in the car with the isofix fitted on them as part of the same unit. This seat will last approximately until age 4 years old.
Group 1 - These are from 9Kg to 18-20Kg and have a height limit of 105cm. These seats stay fixed in the car with the isofix fitted on them as part of the same unit or you can get the same brand seat as your isofix base from the infant carrier and put it on there. This seat will last approximately until age 4 years old.
Group 2/3 - This is also known as a high back booster. These seats are from 15Kg to 36Kg and a height limit of 135 - 150cm. These are forward facing car seats that use the car seat belt as the safety restraint. This is the last car seat you will need, once your child reaches either the weight limit or 135cm they do not need to be in a child seat although you might choose to keep them in the seat until they reach the 150cm height limit if your seat goes that far.
Multi-group car seats 0+/1/2 and 1/2/3 and 0+/1/2/3. These are seats that cover a wide age range and adapt as the child goes through their stages of growth. We aren't such fans of these seats. They do save money and cause less waste because you will go through fewer seats. However, from baby to child sees such massive changes in the body that having one seat shell that can protect a child all the way through we don't think is the best safety solution. They often perform poorly in consumer safety tests.
There is one exception to that and that is the Extended rear facing car seats some of which are Group 0+/1/2. These are always the safest option.