Yōga Sūtra 1.11

अनुभूतविषयासम्प्रमोषः स्मृतिः।

anubhūtaviṣayāsampramōṣaḥ smr̥tiḥ।

[अनुभूत विषय असम्प्रमोषः स्मृतिः।
anubhūta = experienced; viṣaya = topics; asampramōṣaḥ = not slipping away; smr̥tiḥ = is dwelling in memory;]

Experienced topics not slipping away is smriti (dwelling in memories).

Keen interest and emotions are involved when mind wants to dwell in the memories that does not slip away.