Praise be to Allah, and peace and blessings be upon the Messenger of Allah.
The Pond (Al-Hawd) is a great pond belonging to the Prophet ﷺ, which will be in the place of gathering on the Day of Resurrection. The believers from his Ummah will come to it and drink from it. The Prophet ﷺ described it as being a month's journey in length and a month's journey in width, with vessels as numerous as the stars in the sky. Whoever drinks from it once will never feel thirsty afterward.
As for Al-Kawthar, it is a great river that Allah, the Exalted, granted to the Prophet ﷺ in Paradise. Allah says:
﴿Indeed, We have granted you Al-Kawthar.﴾
The difference between them is that the Pond is in the place of gathering, while Al-Kawthar is a river in Paradise. The water of the Pond comes from Al-Kawthar, as two channels flow from it into the Pond on the Day of Resurrection. The believers from the Ummah of Muhammad ﷺ will drink from it.
Thus, Al-Kawthar is in Paradise, while the Pond will be in the place of gathering, and its water comes from Al-Kawthar.
And Allah, the Exalted, knows best.