1)
What are "ha'Batzaros"?
1.
Rashi: That [Hashem] will bring hunger upon them. Radak - it is times of Batzarah (another form of the word Batzores; food is expensive, and there is hunger). This is like "Lo Yibatzer Mehem" (Bereishis 11:6), withholding. Hunger is because rain is withheld 1 . The plural (Batzaros) hints to scarcity of money and of Peros.
2.
Rashi citing Menachem: It is an expression of fortified cities - "u'Mivtzar Misgav Chomosayich" (Yeshayah 25:12).
3.
Radak: Matters in Tzarah (afflictions).
1
Malbim: Yirmeyah prayed about rain being withheld (i.e. that Hashem should not do so - PF).
