Vector is another name for a one-dimensional array. It is used in particular for the arrays with elements of logical types: bit and std_logic (bit_vector and std_logic_vector, respectively).

Examples

signal DataBus : Bit_Vector(7 downto 0);
. . .
DataBus <= "11000011";

Important Notes

Vectors of logical values are not directly transferable to integer values. Neither Standard package nor Std_Logic_1164 package define any conversion functions from logical vector to an integer or vice-versa. Most synthesis tools, however, support such functions (although these functions are tool-specific).
No arithmetic functions are allowed on logical vectors.