"ELA" has something to do with the new limit for business losses.  From the 1040 Instructions:

"Section 461(l) excess business loss adjustments. Enter "ELA" and the taxable amount on the dotted line next to line 21. See Form 461 and its instructions for more information."
https://www.irs.gov/instructions/i1040gi#idm140302174061168

https://www.law.cornell.edu/uscode/text/26/461#l
https://www.irs.gov/pub/irs-dft/f461--dft.pdf
https://www.irs.gov/pub/irs-dft/i461--dft.pdf