A sacrifice is normally something of exceptional cost or worth to you, that you give up to the Gods, and in so doing, make sacred.
In ancient Greek times, this would have encompassed livestock a lot, because they met the above criteria. Giving up sheep, goats, and cattle was, or could be, very costly to the livelihood of the average person.
Yet that willingness to still risk the loss in order to show love, admiration, and request favor from, the Gods, is what made it a sacrifice and a sacred act. The willingness to go long was believed to have grabbed the Gods' attention more.
Today, of course, it doesn't have to pertain to livestock because most people don't live that kind of life anymore. Now our costly sacrifices would be things like money, valuable properties, and our physical time and labor. Even large portions of food and drink, things that take a lot of effort to put together, would be sacrificial.
An offering, however, is a general gift, such as a votive statue, libation, a valuable, or some appropriate foods. They are things that are more readily available and not as costly; easy for pretty much anyone to obtain.
If I give a fresh bar of soap to Aphrodite for Her baths, a libation of olive oil for Athena, or burn incense to Zeus, those would be offerings. This is a bit contradictory to me, because I have normally called all of my burned offerings sacrifices, but to be more accurate, I should use the term offering: my burned offering.
Then again, if it were a huge portion of incense, it may be able to be called sacrifice, but that would take an almost comical pile. Not something normally done.
Often these days, I find myself paying more attention to how I term things, especially publicly. In many cases, I felt the term offering had been used in the religious communities almost to the point of being cliche or monotonous, so I didn't really like using it a lot.
But as a Reconstructionist Hellenist, I find myself more and more concerned with historical accuracy and appropriate piety on a regular basis. It's a lifelong learning experience. Do I think the Gods are petty and care about which term you use? Absolutely not. But the properness sets the human mind correctly.
In the Goodness of the Gods, I'll see you at the next Herm down the road,
Chris Aldridge.