a talent: the largest standard money unit of the ancient world, a weight of silver (or gold) worth thousands of days' wages
A talent was not a coin but the top of the ancient scale of weight and money. Merchants weighed out precious metal, and one talent was a fixed, very heavy amount of it, roughly the value of many years of an ordinary worker's pay. Unless the text says otherwise the metal in view is silver.
In the New Testament the word appears only in Matthew, and always as a sum of money inside a parable. In the story of the servants each is handed a number of talents to invest, and elsewhere a servant owes his king "ten thousand talents," a total so enormous it could never be repaid. In both places the point of the word is its sheer size: a talent is the largest unit there was, so these are staggering amounts.
Its scale stands out against the smaller units the New Testament also names. A talent was worth sixty of the mid-sized unit, the μνᾶ, and thousands of a single day's wage, the δηνάριον, so naming talents signals wealth on a grand scale.