Abbreviated from 低等身デフォルメマスコット ("teitoushin deformed mascot", where "teitoushin" is "low head-to-body ratio").
This refers to mascot-like characters (think along the lines of Hello Kitty) with extremely low head-to-body proportions, frequently hovering around 1:1, as such as their head makes up roughly 50% of their height.

See also

• chibi
• semi-anthro