H1, L1, B1,H2 are different types of non immigrant work visas US offers to all the foreign nationals willing to work on the Us soil.
H1: H1/H1b visa is issued to skilled professionals like engineers, doctors etc. These skilled professionals category does not include management professionals and executives. The purpose of H1 visa is to bring in the foreign nationals into the US when there is no US national that fits the eligibility criteria. The usual time line of processing H1 visa varies from 3 months to 5 months for regular and 15 days for premium. There is a limit on the total number of visas issued in a year. This limit is otherwise called as CAP. Total duration allowed is 6 years.
L1: L1 visas L1A or L1b visas are issued to foreign nationals whose home company has a requirement of a specialist or executive in its US branch for steering the company's branch in US. L1b processing timeline lies between 15 days to 4 months approximately. There is no limit on the number of L1 visas issued in a year. Total duration allowed is 6 years.
B1: A B1 business visa is issued to foreign business executives who comes for a short stay in US on business purposes. The maximum stay on a b1 is 3 months. And the validity can be up to 10 years.
H2: H2a or H2b visas are issued to blue collar jobs and seasonal agriculturalists.