It should be complete within the year.
I'm aiming to reach 100,000 followers by the end of this year.
The assassination must be carried out before the year is over.
Inside the year means by the end of the year. In other words, before the end of this year, or within the year.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.