Popolarismo (Popularism) is a political doctrine conceived by Don Luigi Sturzo, which was the ideological basis for the Italian People's Party and later Christian Democracy. It's a christian-democratic centrist doctrine. It's different to christian left and to social-conservative christian democracy.
The French Popular Democratic Party formed in 1924 was ideologically inspired by the popularism of Sturzo and his Italian People's Party.
Within Christian democracy the use of the name People's Party is widespread, so that European Christian democrats decided to name European People's Party their party in 1976.
"Popular" or "people's" in this context consists of two meanings. The first is the idea that the Christian-democratic parties should try to work towards a policy that is for the good of all the members of society, as opposed to parties that promote the good of a specific group (i.e. class). The second refers to a society where the people live in a kind of harmony, and where people and groups are interested in and care about each other.