How to identify meta key of an input field in WooCommerce

What is meta key of an input field?

<input class="f_age" value="" type="number" name="alg_wc_pif_global_1" id="alg_wc_pif_global_1" placeholder="" required="">

is it alg_wc_pif_global_1

or

_1

or none of them?