Altruism, as observed in populations of organisms, is when an individual performs an action at a cost to themselves (in terms of e.g. pleasure and quality of life, time, probability of survival or reproduction) that benefits, directly or indirectly, another individual, without the expectation of reciprocity or compensation for that action.
ˈɔːltɹuːˌɪzəm, æz əbzˈɜːvd ɪn pˌɑːpjʊlˈeɪʃənz ʌv ˈɔːɹɡənˌɪzəmz, ɪz wɛn ɐn ˌɪndᵻvˈɪdʒuːəl pɚfˈɔːɹmz ɐn ˈækʃən æɾə kˈɔst tə ðɛmsˈɛlvz ɪn tˈɜːmz ʌv ˈiː.dʒˈiː. plˈɛʒɚɹ ænd kwˈɔlᵻɾi ʌv lˈaɪf, tˈaɪm, pɹˌɑːbəbˈɪlᵻɾi ʌv sɚvˈaɪvəl ɔːɹ ɹᵻpɹədˈʌkʃən ðæt bˈɛnɪfˌɪts, dᵻɹˈɛktli ɔːɹ ˌɪndɚɹˈɛktli, ɐnˈʌðɚɹ ˌɪndᵻvˈɪdʒuːəl, wɪðˌaʊt ðɪ ɛkspɪktˈeɪʃən ʌv ɹᵻsɪpɹˈɑːsᵻɾi ɔːɹ kˌɑːmpənsˈeɪʃən fɔːɹ ðæt ˈækʃən.