Invest:
A weather system for which a tropical cyclone forecast center (NHC, CPHC, or JTWC) is interested in collecting specialized data sets (e.g., microwave imagery) and/or running model guidance. Once a system has been designated as an invest, data collection and processing is initiated on a number of government and academic web sites, including the Naval Research Laboratory (NRL) and the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS). The designation of a system as an invest does not correspond to any particular likelihood of development of the system into a tropical cyclone; operational products such as the Tropical Weather Outlook or the JTWC/TCFA should be consulted for this purpose.

http://www.nhc.noaa.gov/aboutgloss.shtml#i

On weather.com and The Weather Channel you may hear us use the term "Invest" (short for Investigation) followed by the numbers 90 through 99 and either the letter "L" for the Atlantic basin systems or "E" for the eastern Pacific systems.

These full labels in the Atlantic would be displayed as Invest 90L, Invest 91L, etc. In the eastern Pacific, you would see Invest 90E, Invest 91E, etc.

This naming convention is used by the National Hurricane Center to identify features they are monitoring for potential future development into a tropical depression or a tropical storm.

https://weather.com/storms/hurricane/news/what-is-an-invest-20120815