Pattern Shell
From PyroGuide
While a sphere could be seen as a pattern, the term Pattern Shell is usually used only to refer to shells that burst in a two dimensional form such as a ring, smiley face or a letter, or to another three dimensional shape such as a Saturn shell or bow tie and ring.
When the pattern is asymmetrical the problem of orientation of the shape in relation to the audience arises, because a shell as it rises is usually free to rotate to any extent. A cord or another mechanism can be attached to the shell so that it only rotates along a single axis as it flies. While this may be very useful for some patterns where it is symmetrical along this axis, it only increases the chance of other shapes facing the audience, without guaranteeing it. For this reason, Shaped shells are usually fired in a group, so that statistically one is likely to face a person no matter were they are viewing from.
Further details can be found in the tutorial for making a Jellyfish Shell.