4. The Terumah is the main gift that every Jew at the time of the Bet Hamikdash (The Temple) was obligated to give to a Kohen before he could eat his produce of grain, fruits or vegetables. See Bemidbar 18:8-12 and Devarim 18:4. It is called Terumah from the Hebrew word Ram which means “to lift” since it had to be separated from a larger quantity by lifting it out of the pile. Hence the English term “heave offering” since the word “heave” means to lift. The Terumah consisted generally of 1/50th of every type of produce that was gathered by that person, although it was possible to give 1/40th if the person felt stingy or 1/60th if he felt especially generous. See Mishna Terumot 4:3. This was known as Terumah Gedolah – The Big Terumah. Besides it when a Levi received his First Tithe (Maaser Rishon) from a regular Israelite he then had to separate from it 1/10th of what he received and give that to a Kohen. That was called Terumat Maaser – the heave offering of the tithe. See Bemidbar 18:26. The Kohen was allowed to eat Terumah only when he was in the state of ritual purity (Tahor). If the Kohen became ritually impure (Tameh), either by touching an impure object or by becoming a Metzora (leprous), then he was not allowed to eat Terumah until he purified himself. Purification basically consisted of waiting a specific amount of days to pass since him becoming impure depending on the impurity he acquired and going to the Mikvah, a ritual pool. In order for the Kohen to become completely pure both things had to happen, the proper number of days to pass and him dipping in the Mikvah, however the Kohen was allowed to dip in the Mikvah during the day of the last day of his purity count and he did not have to wait for the day to complete that coming evening before he could dip. Such a person who has dipped in the Mikvah but still had to wait for the evening for the day to be over is known as a Tevul Yom. The Sages are referring to the time of the evening when the day count was officially over and the Kohen, who was a Tevul Yom, finally became Tahor and was allowed to eat Terumah.