A tea ball (or tea infuser) is a small container made of metal (often steel) pierced with a number of holes, designed to hold a quantity of loose tea for brewing in a cup or teapot.
Tea balls are designed in a number of forms - often ball or egg shaped, but also in the form of a house or a teapot. Normally a small chain or rod is attached to the tea ball for ease of removal once the desired strenght is reached.
A tea strainer serves a similar purpose - being a sieve-like device which holds the tea, and which can be used with a cup or designed for a tea pot.
A wide range of decorative examples are available for those interested in collecting things.