What Does "Interlined" Mean?

In the 1781 indenture of "Dorothea Kline & Al to Nicholas Kline," Nicholas Kline, a son of Michael Kline (my 6th great grandfather), bought land from the other heirs of his father for 400 pounds. This document was typed into a Lancaster County, Pennsylvania deed book.

Lancaster County, Pennsylvania, Deed Book X, page 414 (close up), "Dorothea Kline & Al to Nicholas Kline.
[Note the underlined word "perches" on the 4th line.]

In this typed version, there are two words which are underlined: "perches" on page 414 (see image above) and "share" on page 415.

Lancaster County, Pennsylvania, Deed Book X, page 4147(close up), "Dorothea Kline & Al to Nicholas Kline.
[Note the first few lines which describe the interlined words.]

Following the body of the document is the following comment: Sealed & delivered: written on two several sheets of Paper in the Presence of us: the Word Perches interlined between the eighteenth & nineteenth line & the word share between the twenty third & fourth line.

Random will showing an example of interlined words between lines 24 and 25.

What is "interlined?"

Merriam-Webster defines interlined as "to insert between lines already written or printed." The document above has an example of interlined words between lines 24 and 25.  [Note: The document has been numbered on the far right side of the document.] They are the words that have been squeezed in between the two lines. If you were transcribing this document, you should add a note at the end of this document noting the interlined words. These notes would be in square brackets. For example, you might write: [The words "the presence of us who have hereunto subscribed our names as witnesses thereto in" was interlined between lines 24 and 25.]

Returning to my original document, the clerk's note means that, in the original document, the word "perches" had been interlined or inserted between the 18th and 19th lines, and the word "share" between the 23rd and 24th lines.