Tyrosine (TYR or Y) is one of the more hydrophobic amino acids. Its shape in Foldit is similar to that of phenylalanine, but it has a "stick" on top.
In the Foldit Lua interface, the functions structure.GetAminoAcid and structure.SetAminoAcid use lowercase "y" for tyrosine.
Tyrosine's sidechain contains an oxygen atom which can act as a hydrogen bond accept or donor. See the Sidechain Bonding Gallery and the Sidechain Bonding Table for other sidechain donors and acceptors.
For more, see Tyrosine on wikipedia.