You've basically answered your own question. When some mentions drip feeding links they simply mean building links slower over time instead of all at once. Say you buy 100 backlinks from someone, they can drip feed/schedule these say over the next 30 days, like 3-4 links a day until all 100 links are built. The reason drip feeding is important is because you want to keep your link velocity consistent and going from no links the past few weeks/months to say 100 in a single day doesn't look natural.