In order by importance in the field of linguistics.
If you are looking to understand something more deeply, here are a number of online options for definitions and explanations.
To access corpora from 2016-present that are available for download:
For all MIT users, available corpora are listed by year on the LDC site (MIT Libraries’ access to LDC corpora is limited to corpora published from 2016 on). Note that the corpora available as CDs or DVDs from 2016-present can be accessed by individual title through the Library’s Barton Catalog.