This is a very old interesting Chinese stoneware Longquan Celadon bowl or plate with incised decoration, which we date to the Yuan Dynasty, circa 1300.
The bowl is well potted on a low foot.
The bowl is an olive green colour having a celadon glaze with incised decoration to its centre of what looks like a flower stem and additionally three incised string lines to the outer wall. Unglazed parts fire to a terracotta brown colour as with the base section
The piece is unmarked but for similar pieces see the superb book: Chinese Ceramics by He Li published by Thames & Hudson, 1996; pages 164 to 184.