WFIRST (for Wide Field Infrared Survey Telescope) is planned NASA space observatory for Dark Energy/Cosmology and Extra Solar Planet research, including a Coronagraph for exoplanet Direct Imaging. It will use a surplus National Reconnaissance Office telescope that is the same size as Hubble Space Telescope (2.4m).
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, a mission superseding various dark energy research proposals, including SNAP (Supernova Acceleration Probe), Destiny (Dark Energy Space Telescope), and ADEPT (Advanced Dark Energy Physics Telescope).