What is the meaning of "ibn al-sabīl" (lit. "son of the path")?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. It refers to the guest. [Saʿīd ibn Jubayr, al-Ḍaḥḥāk, Muqātil, al-Farrāʾ, Ibn Qutaybah, al-Zajjāj]
2. It refers to one who passes by you while traveling. [Al-Rabīʿ ibn Anas; also reported from Mujāhid, Qatādah with both views]

It is reported from Imām Aḥmad: It is the one stranded and desiring to reach another land. This is the view preferred by Ibn Jarīr al-Ṭabarī, Abū Sulaymān al-Dimashqī, and Qāḍī Abū Yaʿlā. This is supported by the fact that al-sabīl means the road, and its "son" refers to one journeying on it, who has a right to assistance when in need. Those who hold the first opinion might also be referring to this as, if he is traveling, he is like a guest who has not settled.

1. It refers to one who intends to travel but does not have the means. [Reported by al-Māwardī and others from al-Shāfiʿī]