Assalaamu alaykum. Is this hadith authentic, and what does it mean if it is? "The later generation of Muslims will have a better understanding of Islam than the first."

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

We have not come across a hadeeth with the meaning that you mentioned, but we can authoritatively assert that there is no such hadeeth, and if there is any such hadeeth, then it is false and not authentic.

The meaning of the statement in the question corresponds to the following famous saying that the scholars of Sunnah strongly refuted: “The methodology of the Salaf (righteous predecessors) is safer, but the methodology of the Khalaf (successors) is more knowledgeable and more perfect.”

Many scholars clarified the invalidity of such a statement, among them are Shaykh Ibn Taymiyyah and Shaykh Ibn ‘Uthaymeen .

Shaykh Ibn Taymiyyah said in Dar’ Ta’aarudh al-‘aql wan-Naql, “If someone believes that the successors are more knowledgeable about the truth and its evidence or more capable in debating about it than the Salaf, then they are like those who claimed that they are more knowledgeable, more striving in jihaad (fighting in Allaah's cause), and better at conquering the land than them: both beliefs are the way of those who neither know the truth about the religion nor about the circumstances of the Salaf.” 

Al-Karmi said in Aqaaweel ath-Thiqaat:

“If a person ponders on this statement, he will find that it is absolute ignorance about the Salaf; how is it that the successors would be more knowledgeable about Allaah and His Names and Attributes and more grounded about the Essence of Allaah and His Verses than the foremost among the Muhajireen (Emigrants) and the Ansaar (Helper) and those who followed them exactly in faith among the heirs of the Prophets and pioneers of guidance. It is thanks to them that the Book of Allaah is preserved [as they relied upon it: recited it, acted according to it, and pondered over it], it is thanks to the Book of Allaah that they had excelled and surpassed, and the Book of Allaah mentioned them and praised them; and they recited the Book of Allaah, and Allaah blessed them with knowledge and wisdom, and they had profound knowledge about religious sciences and matters that are not known to the general people; in a way that if the wisdom and knowledge of others is compared to them, the ones who asks for comparison would be ashamed (to compare)."

Allaah knows best.