WFIRST (for Wide Field Infrared Survey Telescope) is a planned NASA space observatory for dark energy/cosmology and extra-solar planet research, including a coronagraph for exoplanet direct imaging. Plans also includes observing gravitational microlensing transients. It will use a surplus National Reconnaissance Office telescope that is the same size as HST (2.4m). Current plans are to launch in the mid 2020s.
The original WFIRST proposal (2011-2012) included construction of a new 1.3 meter telescope. While both variants were under consideration, the now-adopted plan was called WFIRST-AFTA (Astrophysics Focused Telescope Assets).
WFIRST is essentially a rename of the JDEM (Joint Dark Energy Mission) proposal (of circa 2005-2010), a mission plan superseding various dark energy research proposals, including SNAP (Supernova Acceleration Probe), Destiny (Dark Energy Space Telescope), and ADEPT (Advanced Dark Energy Physics Telescope).