What are…
abjects

Meaning: people who have sunk to or exist in a low condition; wretches

This word is used only once in the King James Bible—in Psalm 35:15—and not in more modern translations. The Hebrew word נֵ֫כִים (transliteration: nekeh) meaning smiters, not abjects. This verse is likely an allusion to people who attack with their tongue—slanderers (compare Jeremiah 18:18).

But in mine adversity they rejoiced, and gathered themselves together: yea, the abjects gathered themselves together against me, and I knew it not; they did tear me, and ceased not —Psalm 35:15 KJV

But in my adversity they rejoiced
And gathered together;
Attackers gathered against me,
And I did not know it;
They tore at me and did not cease; —Psalm 35:15 NKJV (New King James Version)

But at my stumbling they rejoiced and gathered themselves together;
The smiters whom I did not know gathered together against me,
They slandered me without ceasing. —Psalm 35:15 NASB

But at my stumbling they rejoiced and gathered;
they gathered together against me;
wretches whom I did not know
tore at me without ceasing —Psalm 35:15 ESV

Compare to Jeremiah 18:18:

Then they said, “Come and let us devise plans against Jeremiah. Surely the law is not going to be lost to the priest, nor counsel to the sage, nor the divine word to the prophet! Come on and let us strike at him with our tongue, and let us give no heed to any of his words.” NASB