NAR stands for "Net Annualised Return". The key figure shows an annualised return on the effectively invested capital over the term of an investment. The NAR calculation thus takes into account the amortisation of the investment and measures the return on the effectively invested capital.
For LEND, the NAR is based on the expected monthly payments (after fees) and it is assumed that capital repayments are reinvested after half of the term.
If you would like to learn even more: We have looked at Net Annualised Return in more detail in a blog post.