The gemara at the beginning of Pesachim has a lengthy discussion attempting to interpret the term "or." Inter alia, the gemara (2b) quotes a beraita regarding the prohibition of work on Erev Pesach: "From when on is work prohibited on the fourteenth (Erev Pesach)? R. Eliezer ben Yaakov says from the time of 'or,' R. Yehuda says from sunrise."
The gemara (Pesachim 4a) records the following question: "Rav Nachman bar Yitzchak asked: If one rents out his house on 14 Nissan, who is responsible to search the premises for chametz? Does the owner (maskir) have to check as it is his chametz in the house; or does the tenant (sokher) have to check as the chametz is now in his possession?"
The Torah [Shemot 12:15] states: "Akh ba-yom ha-rishon tashbitu se'or mi-bateikhem."
This can be understood in two ways:
a. On the first day you shall destroy the leaven from within your homes; or
b. By the first day you must have your homes clear of leaven.
The gemara (Pesachim 5b) quotes a beraita which derives from pesukim that one is forbidden to see one's OWN chametz, but permitted to see that of others' (i.e., non-Jews) and of hekdesh (i.e., that which has been consecrated to the Beit Ha-mikdash).
