noun
free-use notebook; blank notebook
A notebook with unruled or blank pages, often used for drawing, scribbling, or free writing. Commonly associated with children's stationery.
子どもは自由帳に絵を描くのが好きだ。
Children like drawing pictures in a free-use notebook.
自由帳は罫線がないので、自由に使える。
Since a free-use notebook has no ruled lines, you can use it freely.
スケッチブック is a sketchbook primarily for drawing, whereas 自由帳 is a more general blank notebook that can be used for writing or drawing.
Compound of 自由 (free) and 帳 (notebook). The term likely originated from the idea of a notebook that can be used freely without the constraints of ruled lines.