There are three categories of card readers sorted by the type and quantity of the card slots: single card reader (e.g. 1x SD-only), multi card reader (e.g. 9-in-1) and series card reader (e.g. 4x SD-only).
ðɛɹˌɑːɹ θɹˈiː kˈæɾɪɡɚɹiz ʌv kˈɑːɹd ɹˈiːdɚz sˈɔːɹɾᵻd baɪ ðə tˈaɪp ænd kwˈɔntᵻɾi ʌvðə kˈɑːɹd slˈɑːts: sˈɪŋɡəl kˈɑːɹd ɹˈiːdɚ ˈiː.dʒˈiː. wˈʌn ˈɛks ˌɛsdˈiːˈoʊnli, mˈʌltaɪ kˈɑːɹd ɹˈiːdɚ ˈiː.dʒˈiː. nˈaɪnɪn wˈʌn ænd sˈɪɹiz kˈɑːɹd ɹˈiːdɚ ˈiː.dʒˈiː. fˈoːɹ ˈɛks ˌɛsdˈiːˈoʊnli.