Greetings, welcome to the Forums.
This is a Forsythia (Forsythia sp. or hybrid) a deciduous shrub in the Olive Family (Oleaceae). Most of the eleven or so species are native to China, Korea, and Japan, but one species (F. europaea) is native to the western Balkan Peninsula of southeastern Europe.
Many of the most commonly planted Forsythia cultivars are either of the hybrid F. x intermedia, or one of its parents: F. suspensa and F. viridissima.