Abu Ubayd (may Allah have mercy on him) says: 'Umra means that a man says to another man: This house is yours as long as you live, or he says: This house is yours as long as I live. Something similar is also reported from Ata' (may Allah have mercy on him) in explaining 'umra.
Abu Ubaydah (may Allah have mercy on him) says: Regarding ruqba, Abu al-Zubayr (may Allah have mercy on him) said: Ruqba is that a man says: If you die before me, this will return to me, and if I die before you, it is yours.
Qatadah (may Allah have mercy on him) says: Ruqba is that someone says: This is for so-and-so, and if he dies, it is for so-and-so.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 11990