Lady Grey, like its counterpart Earl Grey, is a black tea flavoured with citrus. Whereas Earl Grey adds nothing other than bergamot, Lady Grey adds orange, lemon, and various other citrus flavours, although it doesn't usually contain bergamot.
The resultant brew tastes kind of like English breakfast tea mixed with dissolved orange Tic-Tacs, if I may be so bold, though I find its flavour to be unique. It is appropriately named, as it seems to be a softer, more flowery version of Earl Grey, though it is unclear if it was named for Earl Grey's wife (if he indeed even had one), or whether she was soft and flowery.
Like all black teas, Lady Grey is quite caffeinated, and as far as I know only Twinings makes a decaffeinated brew. Also, like most black teas, this one isn't black; it has a deep, dark mahogany colour, which stays clear until milk or cream is added.
Despite Lady Grey's wide availability (it's available in most grocery stores), it doesn't seem to be very popular.
Ideally, any love interest, however fleeting, of Captain Jean-Luc Picard would enjoy this brew.