Since it's unstated, you get the whole one piece wiki

One Piece Statistics Japanese Name: ひとつなぎの大秘宝ワンピース Romanized Name: Wan Pīsu Official English Name: One Piece First Appearance: Chapter 2; Episode 1 (mentioned)[1] Owner: Joy Boy (former) Gol D. Roger (former) For other uses of this name, see One Piece (Disambiguation). One Piece is the name the world gave to all the treasure gained by the Pirate King Gol D. Roger.[2] At least a portion of it once belonged to Joy Boy during the Void Century.[3] The treasure is said to be of unimaginable value, and is currently located on Laugh Tale, the final island of the Grand Line.

The One Piece is the driving goal of Monkey D. Luffy and his crew, as well as that of multiple other pirates, who all seek to claim the treasure in order to become the next Pirate King, following Roger's dying words at his execution.

The Great Treasure At some point during the Void Century, a man named Joy Boy came across an island located at the end of the Grand Line. Here, he left behind a treasure of unimaginable value,[3] however, Dr Vegapunk theorized that the person who would find it might not be the one Joy Boy initially was hoping for.[4] Stories of this treasure on the final island piqued the interest of Gol D. Roger, and he took the World Government forbidding exploration of the island as evidence of it being real.[5]

Only the members of the Roger Pirates crew that journeyed to the island learned what exactly the treasure consists of. Upon arriving on the island and seeing Joy Boy's treasure, the Roger Pirates simply began to laugh. Roger described it as a "tale full of laughs", which gave him the idea to name the final island "Laugh Tale".[3] Sometime after the Roger Pirates' discovery, the world at large would begin to refer to Roger's treasures as the "One Piece".[2]

Before Roger was executed, he announced to the world that this great treasure could be claimed by anyone who could reach it, thereby starting the Great Age of Pirates.

The closest the Straw Hat Pirates have ever come to finding out the nature of the One Piece was during the Sabaody Archipelago Arc, when Usopp tried to ask Silvers Rayleigh about it. However, Luffy stopped him on the grounds that learning about it from someone else would defeat the purpose of their adventures and that becoming the Pirate King would have little merit if he already knew anything about the One Piece.[6]

After decades of speculations and doubts, the treasure's existence was confirmed by Whitebeard with his last breath. He mentioned that "a grand battle will engulf the entire world" and "the world will be shaken to its core" when the One Piece is found.[7]

During the Wano Country Arc, Big Mom had an internal monologue expressing the idea that "some of" the One Piece might be located in Wano Country rather than Laugh Tale. This has yet to be elaborated on further.[8]

During a worldwide broadcast happening in the Egghead Arc, Vegapunk confirmed the existence of the One Piece and stated that whoever would claim it would have the power to decide the fate of the world.[9]

Translation and Dub Issues In the original manga, the term "One Piece" (ワンピース, Wan Pīsu?) is often accompanied by an additional string of text translating roughly to "the great hito-tsunagi treasure" (ひとつなぎの大秘宝, Hito-tsunagi no Dai-hihō?), initially as a separate descriptor[1] and later as a base-text directly glossed with the "One Piece" katakana.[10]

The exact meaning of "hito-tsunagi" has not yet been clarified, and there are three possible readings:

That it should be read as "一つなぎ" - a more or less literal Japanese translation of "(in) one piece". That it should be read as "人繋ぎ" - a phrase roughly translating to "the rope linking all men". That it should be read as "hitotsu-nagi" or "一つ凪" - a phrase roughly translating to "one sea at peace".